NM modified version that displays selectable cycle of 4ths or random notes on the first beat of the bar. Also has a mute button.
This application shows how to use a collaboration between a setTimeout scheduler and the Web Audio scheduler to properly implement rock-solid timing for audio applications.
Check it out, feel free to submit issues or requests, fork, submit pull requests, etc.
The live app is at http://webaudiodemos.appspot.com/metronome/index.html.
-Chris